A failing Restore job's logs show that the tape drive had a problem reading the data that was stored on the tape, such as below:
-- Job Message 2012/09/11 14:17:54 173 Media NV_Server Job has been assigned media 'netvault 28 Mar 10:33-1' <calscrew backup> in 'PowerVault 110T:netvault'
-- Information 2012/09/11 14:17:54 173 Media NV_Server Media identified as 'netvault 28 Mar 10:33-1' <calscrew backup>
-- Error 2012/09/11 14:49:47 173 Media NV_Server netvault 2-0.6.0 (QUANTUM ULTRIUM 3): had media error
-- Error 2012/09/11 14:50:28 173 Data Plugin CLIENT Fatal error while processing item : 'Error reading from media'
These errors originate directly from the tape library or tape drive, not from NetVault, so there may be a problem with the tape that contains the data or a problem with the Drive used for the restore, which would be logged as the drive used for that particular run of the Restore job earlier in the log.
If you have multiple drives, try placing the problematic tape into a different drive first, then kick off the Restore job again.
If the job fails again with the same 'Error reading from media' message, then it's fairly certain that the problem is with the tape.
If the job succeeds, then the problem would lie with the original drive used for the failed Restore. In that case, try cleaning the drive or contacting your hardware vendor for assistance diagnosing the problem with the hardware.
Another suggestion would be to log into the tape library's web GUI, if available, and check for more detailed information on the error that occurred at the time that the 'Error reading from media' message was seen in the logs.
There may also be additional errors logged to your OS. Windows would log these in the NVBU Server's Event Viewer's System or Application logs. Linux/Unix/Mac systems would log them under /var/log/messages.
In any case, the errors originate directly from your hardware and not from NetVault.